Electrical and mechanical system for the re-recording of sound film



Oct. 5, 1937. 0. K. KOLB 2,094,745- ELECTRICAL AND MECHANICAL SYSTEM FOR THE RE-RECORDING OF SOUND FILM;

Filed Aug. 5, 1936 2 Sheets-Sheet' 1 PHOTO 0- CELL 0 OSGILLO- Q GRAPH POLARIZ|NG PANEL FIG. 1

INVENTOR. 07m KURT Irma ATTORNEY.

0. K. KOLB ELECTRICAL AND MECHANICAL SYSTEM FOR THE RE-RECORDING OF SOUND FILM Filed Aug. 3, 1936 2 Sheets-Sheet 2 a E 5 R E P 5 E L C Y c 4000 4500 CYCLES PER sec.

5 FIG. 4

I 56 CYCLES PER 550.

- INVENTOR. 0 077a KURT KOLB ATTORNEY.

Patented Oct. 5, 1937 UNITED STATE ATE ELECTRICAL AND ME CHANIGAL SYSTEM FOR THE RE-RECORDING OF SOUND FILM Otto Kurt Kolb, Chiswick, London, England Application August 3, 1936, Serial No. 94,012 In Great Britain June 10, 1936 3 Claims.

This invention relates to filter systems for use in the electrical re-recording of sound.

It is known in the art that whilst the sound track on a large scale film, for example of 35 mm. standard type, can accommodate adequately sound track undulations or variable density bands representing high sound frequencies, when such a large scale film bearing a sound record track is, by optical printing, or normal electrical rerecording processes impressed on a copy film of reduced scale, for example, of 16 mm. stand ard type, owing to the small scale of the copy, such high frequency undulations, or varying density bands are congested and tend to coalesce or overlap with a consequent deterioration of the overall intelligibility or purity of the sound reproducible from such a film.

According to the invention, when a master film is photo-electrically reproduced and the resulting phonic current is carried through a sound recording apparatus for the purpose of re-recording a sound sequence on a copy film or positive of reduced scale, a filter system is introduced between the photoelectric reproducing device and the re-recording apparatus 2. Such filter is designed to cut off or eliminate substantially or totally all sound components of a frequency exceeding a predetermined upper limit.

By this means, whilst the copy film receives in due measure an impression of all those auditory components of the sound sequence which it is physically possible to record on it with clarity and faithfulness, the components of the sound, which exceed the fixed upper limit, which cannot physically be satisfactorily accommodated, and which do not contribute, therefore, any additional value to the sound record, but, on the contrary, tend to obscure it, are eliminated.

Certain defects may exist in the master sound film due either to the grain of the emulsion or to recording defects, especially in the upper register, and tend to be exaggerated in the substandard or reduced copies.

In the re-recording of sub-standard films from standard films, the filtering means, constructed according to the invention, by the elimination of the higher frequencies above the predetermined limit, renders the copies obtained from such master films sensibly free of such faults.

For the further explanation of the nature of the invention reference will be made, as examples, to the arrangements shown in the accompanying drawings, Figs. 1, 2, 3 and 4.

In Fig. 1 the filtering means is schematically exemplified as comprising two rejector loop circuits L, C and Li, Cl, these being in series with an interposed inductance L2, the junctions L L|* between each rejector loop and the inductance being connected to teed-off condensers C2 and 03, respectively. The values of such a circuit can advantageously be as follows:

L and Ll=0.01275 henry each C and Cl=0.063 microfarad each C2 and C3=0.0944 microfarad each The transmission characteristic of such a filter is represented by the graph shown in Fig. 2. Herein, the ordinates represent levels of transmission logarithmically arranged, whilst the abscissae represent frequency in cycles per second.

It will be seen that the transmission remains level until a frequency of approximately 4,000 cycles per second is reached, and dropping rapidly, gives a practically complete cut-oil? at a limiting frequency of approximately 4,500 cycles per second.

As shown in Fig. 3, recording oscillograph .3, constituting in itself a mechanical filter, is constructed in the form in which a loop of wire 4 or strip carries a mirror 5 and is located in oil between suitably opposed pole pieces 6.

The oscillograph 3 so constructed is, for the purpose of carrying out the invention, given an operative characteristic of the type exemplified in Fig. 4 of the drawings. Herein, ordinates represent logarithmically levels of vibration response with constant current input, whilst abscissae represent frequencies. It will be seen that the response of the oscillograph is purposely rendered substantially constant until a frequency of 3000 cycles per second is reached, when a resonance is manifested by the peak of the curve at approximately 3500 cycles per second, followed by a rapid cut-off of the mirror vibrations at the upper limit of approximately 4500 cycles per second.

The invention may be embodied in diverse constructional forms without departing from its essential nature as defined in the appended claims.

What I claim is:

1. In a sound re-recording system for the production of substandard films from standard films, a photoelectric reproducing device, a sound re-recording apparatus, and a filter system between said device and apparatus eliminating substantially all frequency components of a sound sequence exceeding a fixed upper limit.

2. In a system according to claim 1 and in which said filter system comprises an electrical filter eliminating all phonic current frequency components exceeding a limiting frequency of approximately 4000 cycles per second at which frequencies the filter produces a practically infinite attenuation.

3. In a system according to claim 1 andin which said filter system comprises an oscillograph, and calibrated adjustable means associated with said oscillograph to damp out vibrations above a limiting value of approximately 4000 cycles.

OTTO KURT KOLB. 

